WDC WD20EARS and 4k sector size

[Herbert Poetzl <herbert@13thfloor.at>]

I recently bought the WDC WD20EARS-00MVWB0 because it
was really cheap for a drive with 64 MB cache, and I
wanted to try out a 4k sector size disk ...

Now the drive performs quite well, is rather silent
and doesn't use much power or produce much heat, but
at first I didn't find anything in Linux indicating
that this drive would actually use 4k sectors.

To shorten things, I asked around on IRC, had a chat
with some other folks, found a jumper description on
the WD site talking about an 'Advanced Format' jumper
and finally contacted WD in a lengthy email thread.

The results of all this are:

 - the drive doesn't report 4k sectors at all, not
   even as physical sector size.

 - the 'Advanced Format' jumper shifts access to the
   the drive by one sector.

I did some tests to verify that, and I can confirm
the behaviour of the jumper in question with certain
benchmark tests (using dm and bonnie++) with and
without the jumper in place.

My question now is, how can I tell the kernel that
this drive actually has 4k physical sectors and that
it would be a smart thing to send requests in some 
kind of 4k I/O chunks?

Many thanks in advance,
Herbert

PS: if somebody is interested in the tests done to
verify the jumper, please let me know ...